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22 OCTOBER 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 10 CATHODIC PROTECTION E Ever since Sir Humphry Davy first ap- plied cathodic protection (CP) to pro- tect the British Navy's warships from corrosion, the benefits of CP in ma- rine applications have been adopted in a wide range of applications. One of the areas where CP is commonly applied to marine structures for cor- rosion protection is the steel piling systems on jetties and piers. This article discusses the design and im- plementation of CP on a newly con- structed jetty in Surabaya, Indonesia, and includes a comparison of key factors for commonly used galvanic (aluminum) anodes and impressed current (titanium with mixed metal oxide) anodes. Every cathodic protection (CP) design E c Every cathodic protection (CP) design E protection (CP) design ef for t b egins with a basic deci sion of E or t b egins with a basic deci sion of w h e th er to u s e galv a ni c a n o d e s th at E h e th er w h e th er to u s e galv a ni c a n o d e s th at E to u s e galv a ni c a n o d e s th at operate on the natural potential difference E natural operate on the natural potential difference E potential difference between the anode and the structure, or E tween between the anode and the structure, or E the between the anode and the structure, or E anode between the anode and the structure, or E and the structure, or impressed current anodes with an external E pressed impressed current anodes with an external E current anodes with an external power supply that can provide a range of E wer power supply that can provide a range of E supply that can provide a range of d r iv i n g v o lt a ge s . Th e ke y di f feren c e s E s . Th e ke y di f feren c e s b etw e en b etw e en an impre ssed current an o d e E an impre ssed b etw e en an impre ssed current an o d e E current an o d e sy st e m a n d a ga lv a n i c a n o d e sy st e m include anode consumption rates, current density (CD) limits, and driving voltage. Anode Consumption Rates Aluminum alloy anodes are typically used in seawater galvanic systems, and they have a nominal capacity of 2,000 A-h/kg. Impressed Current Anode Systems for Jetty Piling Protection Ted Huck, MATCOR, Inc., Chalfont, Pennsylvania S H aile SH Javia, SGB Scaffolding and Industrial Services Private Limited, Gujarat, India Today's standard for impressed current CP (ICCP) applications is a titanium anode with a mixed metal oxide (MMO) coating. These anodes are dimensionally stable with e xc e pti on al ly l ow c on su mpti on rat e s (~2 million A-h/kg or 1,000 times the equiva- lent capacity of aluminum anodes), resulting in much smaller anodes with much longer anode life—often well in excess of 30 years. Current Density Limit Anode manufacturers typically specify maximum CD for efficient operation in spe- cific environments. Aluminum alloy anodes can operate at a maximum CD discharge limit of 15 A/m 2 but are typically designed to operate at a much lower CD. Impressed current MMO anodes are capable of operat- ing at significantly higher CD discharge rates—up to 500 A/m 2 ; however, in most cases, the operating levels are much lower. Th e high er C D range of MMO anodes allows the designer to use fewer anodes and operate those anodes at much higher outputs. Driving Voltage Aluminum alloy anodes have a natural potential of ~ –1.05 V relative to a silver/ silver chloride (Ag/AgCl) reference elec- trode in seawater. As with all galvanic anodes, aluminum anodes do not require an external power source. The initial driv- ing voltage is the difference between the characteristic potential of the anode and the free corrosion potential of the struc- ture; h ow e v er, thi s driv in g v o lt a ge i s reduced as th e str ucture i s polari zed .